Our parent project aims to develop a small, lightweight, battery-powered collector suitable for time-resolved personal and micro-environmental monitoring of the chemical constituents of airborne particles. This revision submission aims to enhance that technology through the development of an air-to-air particle concentrator that is effective for ultrafine and nanometer-sized particles as well as fine particles. This concentrator can serve as a suitable inlet for the miniature particle collector being developed under the parent project;and that will also be suitable for many other exposure, toxicology and ultrafine particle characterization applications. The approach utilizes our patented water condensation technology, wherein particles as small as 0.003 5m can be encapsulated in a 3-5m water droplet in a differentially- diffusive, laminar flow. Once enlarged the droplets are aerodynamically focused through converging flow in a sharp-edged orifice. Because residence times of the droplets are short, chemical artifacts are minimized. With this approach we anticipate the focusing and 10-fold air-to-air concentration of particles as small as 0.008 5m. PUBLIC HEALTH RELEVANCE: Ultrafine and fine particles are ubiquitous in our environment, yet epidemiological studies have shown statistically significant relationships between their concentrations and rates of morbidity and mortality. Ultrafine particles are specifically implicated. Proposed is the development of an instrument to concentrate ultrafine and fine airborne particles that will aid in the assessment their toxicity and their levels in the air we breathe.